The invention relates to a drive assembly for auxiliary units of an internal combustion engine of a motor vehicle. The units may be mounted at an end wall of the internal combustion engine, especially coaxially relative to the crankshaft. Two switchable gear stages are between the input shaft driven by the crankshaft and the output shaft driving the auxiliary units, with gear changing effected by actuating a friction coupling.
Drive assemblies of this type are known from EP 0 123 580 B1. It is the purpose of such assemblies to ensure that even close to the idling speed, the major auxiliary units, such as the water pump, generator, possibly the hydraulic pump for power steering and the air conditioning compressor are supplied with sufficient power, e.g. are driven at a relatively high speed, On the other hand, the assemblies ensure, at an increased engine speed for the purpose of reducing fuel consumption, the driving speed and thus the power consumption of the auxiliary units are reduced because, as compared to operating conditions close to the idling speed, the power requirements of the auxiliary units are not increased accordingly. On the contrary, it is sufficient in such cases to drive the auxiliary units at a speed which is reduced as compared to the engine speed. The planetary gear unit used in such cases is actuated by a solenoid integrated into the housing of the drive assembly, with a direct connection between the driveshaft and the drive assembly housing accommodating a pulley being effected in a power-less way by pressure springs.
Because the solenoid is integrated into the drive assembly housing, the entire assembly has to be replaced if the solenoid fails, as a result of which repair costs are very high. The assembly described is inadequately protected against the environment so that failure is likely to occur.
Furthermore, it is disadvantageous if, for the operating position itself, only one of the two gear stages requires power on a permanent basis. This applies in view of the fact that the electric system of motor vehicles has already reached its loading limits, which means that its own requirements partially destroy the justification for the expense of providing a two-gear drive assembly for the auxiliary units with the objective of saving energy.